During the past two decades, Pseudomonas aeruginosa has been recognized as a pathogen which causes between 10% and 20% of infections in most hospitals. Pseudomonas infection is especially prevalent among patients with burn wounds, cystic fibrosis, acute leukemia, organ transplants, and intravenous-drug addiction. P. aeruginosa is a common nosocomial contaminant, and epidemics have been traced to many items in the hospital environment. Patients who are hospitalized for extended periods are frequently affected by this organism and are at increased risk of developing infection. The most serious infections include malignant-external otitis, endophthalmitis, endoconditis, meningitis, pneumonia, and septicemia. The likelihood of recovery from Pseudomonas infection is related to the severity of the patient's underlying disease process. The reported mortality for P. aeruginosa pneumonia is as high as 50-80%. Even with the development of newer antibiotics, resistance remains a problem necessitating combined antibiotic treatment for severe P. aeruginosa infections.
Various therapies for the management of severe P. aeruginosa infections have been evaluated for many years, with particular attention focused on virulence factors. As with most bacterial pathogens, virulence of P. aeruginosa is multifactorial and is the product of many interacting variables, involving both the bacterium and the host. Evidence suggests that the initial event in infection is the adherence of microorganisms to epithelial cells of mucosal surfaces (Bleachy). Organisms that are unable to adhere to mucosal surfaces fail to colonize because they are removed by the secretions that bathe the mucosal surfaces (Bleachy). The adherence process is dependent upon the specific recognition between bacteria and epithelial cells, mediated through adhesin molecules present on the bacterial cell surface and receptors present on target cells.
Molecules which have been identified as adhesins in P. aeruginosa include alginate and pilus proteins. P. aeruginosa can utilize both pili and alginate (the principle component of the P. aeruginosa capsule) as adhesins to mediate attachment to human respiratory epithelial cells (Doig). Pili have been identified as an important adhesive factor for buccal cells (Woods 1980), damaged tracheal epithelium (Ramphal 1984), and mucous proteins (Ramphal 1987). In particular, a specific peptide domain of the pilus protein has been recognized as a determinant of the adhesive properties of these P. aeruginosa.
Gangliosides , and in particular, gangliotriosylceramide (GgO.sub.3 ; GalNac.beta.1-4Gal.beta.1-4Glc.beta.1-1Cer), gangliotetraosylceramide (GgO.sub.4 ; Gal.beta.1-3GalNAc.beta.1-4Gal.beta.1-4Glc.beta.1-1Cer), and lactosylceramide (LacCer; Gal.beta.1-4Glc.beta.1-1Cer) have been identified as possible receptors for P. aeruginosa (Baker, Krivan), but the adhesin or adhesins responsible for this specificity have not been identified. P. aeruginosa can utilize both pili and alginate (the principle component of the P. aeruginosa capsule) as adhesins to mediate attachment to human respiratory epithelial cells (Doig). However, strains exist which lack both pili, and ability to synthesize alginate and which still retain the capacity to attach to epithelial cells, thereby suggesting the existence of additional adhesin molecules.
Earlier filed co-pending and co-owned U.S. patent applications (Ser. Nos. 638,492 and 344,565) disclose P. aeruginosa peptides derived from the C-terminal region of the P. aeruginosa pilin protein, and specifically, the C-terminal region which includes two Cys residues and the intervening amino acid residues. The derived region of representative peptides vary in length between 14 and 19 amino acid residues, including the two Cys residues, and are prepared in both oxidized (disulfide-linked) and reduced (non-cyclized) form. The peptides (in both reduced and oxidized form) were shown to have the following properties:
(a) ability to bind to human tracheal epithelial cells (TECs) and human buccal epithelial cells (BECs);
(b) ability to inhibit binding of Pseudomonas pilin peptide to tracheal epithelial cells (TECs) and buccal epithelial cells (BECs);
(c) ability to elicit serum antibodies which are immunoreactive with Pseudomonas pilin peptide;
(d) ability to elicit serum antibodies which block binding to Pseudomonas pilin peptide to BECs; and
(e) ability to inhibit binding of unrelated bacterial and fungal organisms to human BECs and/or tracheal epithelial cells (TECs).
It was further shown, in studies conducted in support of these applications, that monoclonal antibodies prepared against the Pseudomonas-derived peptide were effective in blocking fungal cell adherence to BECs.
It has now been discovered that exoenzyme S (Exo S), a bacterial toxin having ADP ribosyl transferase activity which is present on the surface of P. aeruginosa cells, also binds to BECs with a specificity which is similar to that exhibited by bacterial cells. Antibodies which are directed against the pilus peptide domain earlier recognized as a determinant of bacterial binding cross react with purified Exo S. The binding region includes a segment of the amino acid sequence of Exo S having about 60-70% sequence homology with the above pilus peptide domain found to be a determinant of bacterial binding to target cells.
These combined findings show that the Exo S-derived peptide, and antibodies produced in response to the peptides, are capable of inhibiting infections in which the infecting microorganism has surface proteins which are immunologically crossreactive with antibodies produced against the peptide region of Exo S protein.